Conventionally, audio data included in a piece of music is analyzed to automatically extract the tempo of the music for use in preparing a written composition or adapting a musical composition. The Japanese Patent Application Laid Open No. 2002-116754 discloses a technique of extracting a tempo from such a written composition.
The technique disclosed in the above patent document is to acquire audio data in a music composition as time-series data and calculate the autocorrelation of the audio data to detect peak positions in the audio data and acquire candidates for a tempo, while analyzing the beat structure of the music composition on the basis of the peak positions in the autocorrelation pattern and levels of the peaks to estimate a most appropriate tempo on the basis of the tempo candidates and the result of beat structure analysis.
Using the technique disclosed in the above patent document, even any person having no pure knowledge of the music can extract an intended musical tempo relatively simple and accurately.
Note here that there has recently been proposed to detect the tempo of a musical composition to be reproduced and provide information corresponding to the detected tempo or make various kinds of control correspondingly to such a detected tempo in an in-vehicle audio system (Car Stereo) or home audio system.
With the technique disclosed in the aforementioned patent document, vast complicated computational operation is required for calculation of the autocorrelation of audio data and analysis of beat structure, and thus the load to the CPU (central processing unit) making such an operation is large.
On this account, the technique disclosed in the patent document is not suitable for employment in a relatively small-scale in-vehicle or home audio system as the case may be. Also, in case the technique in question is adopted, it becomes necessary to use a CPU having a high processing power and a memory having a larger capacity, which will lead to an expensive audio system.